/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.swak.codec;

import java.util.Arrays;

import com.swak.utils.StringUtils;

/**
 * Abstract superclass for Base-N encoders and decoders.
 *
 * <p>
 * This class is thread-safe.
 * </p>
 *
 * @author lifeng copy
 * @version $Id: BaseNCodec.java 1465182 2013-04-06 04:03:12Z ggregory $
 */
public abstract class BaseNCodec {

	/**
	 * Holds thread context so classes can be thread-safe.
	 * <p>
	 * This class is not itself thread-safe; each thread must allocate its own copy.
	 *
	 * @since 1.7
	 */
	public static class Context {

		/**
		 * Place holder for the bytes we're dealing with for our based logic.
		 * Bitwise operations store and extract the encoding or decoding from this variable.
		 */
		int ibitWorkArea;

		/**
		 * Place holder for the bytes we're dealing with for our based logic.
		 * Bitwise operations store and extract the encoding or decoding from this variable.
		 */
		long lbitWorkArea;

		/**
		 * Buffer for streaming.
		 */
		byte[] buffer;

		/**
		 * Position where next character should be written in the buffer.
		 */
		int pos;

		/**
		 * Position where next character should be read from the buffer.
		 */
		int readPos;

		/**
		 * Boolean flag to indicate the EOF has been reached. Once EOF has been reached, this object becomes useless,
		 * and must be thrown away.
		 */
		boolean eof;

		/**
		 * Variable tracks how many characters have been written to the current line. Only used when encoding. We use
		 * it to make sure each encoded line never goes beyond lineLength (if lineLength > 0).
		 */
		int currentLinePos;

		/**
		 * Writes to the buffer only occur after every 3/5 reads when encoding, and every 4/8 reads when decoding. This
		 * variable helps track that.
		 */
		int modulus;

		Context() {
		}

		/**
		 * Returns a String useful for debugging (especially within a debugger.)
		 *
		 * @return a String useful for debugging.
		 */
		@SuppressWarnings("boxing") // OK to ignore boxing here
		@Override
		public String toString() {
			return String.format(
					"%s[buffer=%s, currentLinePos=%s, eof=%s, ibitWorkArea=%s, lbitWorkArea=%s, "
							+ "modulus=%s, pos=%s, readPos=%s]",
					this.getClass().getSimpleName(), Arrays.toString(buffer), currentLinePos, eof, ibitWorkArea,
					lbitWorkArea, modulus, pos, readPos);
		}
	}

	/**
	 * EOF
	 *
	 * @since 1.7
	 */
	static final int EOF = -1;

	/**
	 * MIME chunk size per RFC 2045 section 6.8.
	 *
	 * <p>
	 * The {@value} character limit does not count the trailing CRLF, but counts all other characters, including any
	 * equal signs.
	 * </p>
	 *
	 * @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045 section 6.8</a>
	 */
	public static final int MIME_CHUNK_SIZE = 76;

	/**
	 * PEM chunk size per RFC 1421 section 4.3.2.4.
	 *
	 * <p>
	 * The {@value} character limit does not count the trailing CRLF, but counts all other characters, including any
	 * equal signs.
	 * </p>
	 *
	 * @see <a href="http://tools.ietf.org/html/rfc1421">RFC 1421 section 4.3.2.4</a>
	 */
	public static final int PEM_CHUNK_SIZE = 64;

	private static final int DEFAULT_BUFFER_RESIZE_FACTOR = 2;

	/**
	 * Defines the default buffer size - currently {@value}
	 * - must be large enough for at least one encoded block+separator
	 */
	private static final int DEFAULT_BUFFER_SIZE = 8192;

	/**
	 * Mask used to extract 8 bits, used in decoding bytes
	 */
	protected static final int MASK_8BITS = 0xff;

	/**
	 * Byte used to pad output.
	 */
	protected static final byte PAD_DEFAULT = '=';

	/**
	 * instance variable just in case it needs to vary later
	 */
	protected final byte PAD = PAD_DEFAULT;

	/**
	 * Number of bytes in each full block of unencoded data, e.g. 4 for Base64 and 5 for Base32
	 */
	private final int unencodedBlockSize;

	/**
	 * Number of bytes in each full block of encoded data, e.g. 3 for Base64 and 8 for Base32
	 */
	private final int encodedBlockSize;

	/**
	 * Chunksize for encoding. Not used when decoding.
	 * A value of zero or less implies no chunking of the encoded data.
	 * Rounded down to nearest multiple of encodedBlockSize.
	 */
	protected final int lineLength;

	/**
	 * Size of chunk separator. Not used unless {@link #lineLength} > 0.
	 */
	private final int chunkSeparatorLength;

	/**
	 * Note <code>lineLength</code> is rounded down to the nearest multiple of {@link #encodedBlockSize}
	 * If <code>chunkSeparatorLength</code> is zero, then chunking is disabled.
	 *
	 * @param unencodedBlockSize   the size of an unencoded block (e.g. Base64 = 3)
	 * @param encodedBlockSize     the size of an encoded block (e.g. Base64 = 4)
	 * @param lineLength           if &gt; 0, use chunking with a length <code>lineLength</code>
	 * @param chunkSeparatorLength the chunk separator length, if relevant
	 */
	protected BaseNCodec(final int unencodedBlockSize, final int encodedBlockSize, final int lineLength,
			final int chunkSeparatorLength) {
		this.unencodedBlockSize = unencodedBlockSize;
		this.encodedBlockSize = encodedBlockSize;
		final boolean useChunking = lineLength > 0 && chunkSeparatorLength > 0;
		this.lineLength = useChunking ? (lineLength / encodedBlockSize) * encodedBlockSize : 0;
		this.chunkSeparatorLength = chunkSeparatorLength;
	}

	/**
	 * Returns true if this object has buffered data for reading.
	 *
	 * @param context the context to be used
	 * @return true if there is data still available for reading.
	 */
	boolean hasData(final Context context) { // package protected for access from I/O streams
		return context.buffer != null;
	}

	/**
	 * Returns the amount of buffered data available for reading.
	 *
	 * @param context the context to be used
	 * @return The amount of buffered data available for reading.
	 */
	int available(final Context context) { // package protected for access from I/O streams
		return context.buffer != null ? context.pos - context.readPos : 0;
	}

	/**
	 * Get the default buffer size. Can be overridden.
	 *
	 * @return {@link #DEFAULT_BUFFER_SIZE}
	 */
	protected int getDefaultBufferSize() {
		return DEFAULT_BUFFER_SIZE;
	}

	/**
	 * Increases our buffer by the {@link #DEFAULT_BUFFER_RESIZE_FACTOR}.
	 *
	 * @param context the context to be used
	 */
	private byte[] resizeBuffer(final Context context) {
		if (context.buffer == null) {
			context.buffer = new byte[getDefaultBufferSize()];
			context.pos = 0;
			context.readPos = 0;
		} else {
			final byte[] b = new byte[context.buffer.length * DEFAULT_BUFFER_RESIZE_FACTOR];
			System.arraycopy(context.buffer, 0, b, 0, context.buffer.length);
			context.buffer = b;
		}
		return context.buffer;
	}

	/**
	 * Ensure that the buffer has room for <code>size</code> bytes
	 *
	 * @param size    minimum spare space required
	 * @param context the context to be used
	 */
	protected byte[] ensureBufferSize(final int size, final Context context) {
		if ((context.buffer == null) || (context.buffer.length < context.pos + size)) {
			return resizeBuffer(context);
		}
		return context.buffer;
	}

	/**
	 * Extracts buffered data into the provided byte[] array, starting at position bPos, up to a maximum of bAvail
	 * bytes. Returns how many bytes were actually extracted.
	 * <p>
	 * Package protected for access from I/O streams.
	 *
	 * @param b       byte[] array to extract the buffered data into.
	 * @param bAvail  amount of bytes we're allowed to extract. We may extract fewer (if fewer are available).
	 * @param context the context to be used
	 */
	void readResults(final byte[] b, final int bAvail, final Context context) {
		if (context.buffer != null) {
			final int len = Math.min(available(context), bAvail);
			System.arraycopy(context.buffer, context.readPos, b, 0, len);
			context.readPos += len;
			if (context.readPos >= context.pos) {
				// so hasData() will return false, and this method can return -1
				context.buffer = null;
			}
		}
	}

	/**
	 * Checks if a byte value is whitespace or not.
	 * Whitespace is taken to mean: space, tab, CR, LF
	 *
	 * @param byteToCheck the byte to check
	 * @return true if byte is whitespace, false otherwise
	 */
	protected static boolean isWhiteSpace(final byte byteToCheck) {
		switch (byteToCheck) {
		case ' ':
		case '\n':
		case '\r':
		case '\t':
			return true;
		default:
			return false;
		}
	}

	/**
	 * Encodes an Object using the Base-N algorithm. This method is provided in order to satisfy the requirements of
	 * the Encoder interface, and will throw an EncoderException if the supplied object is not of type byte[].
	 *
	 * @param obj Object to encode
	 * @return An object (of type byte[]) containing the Base-N encoded data which corresponds to the byte[] supplied.
	 * @throws EncoderException if the parameter supplied is not of type byte[]
	 */
	public Object encode(final Object obj) throws EncoderException {
		if (!(obj instanceof byte[])) {
			throw new EncoderException("Parameter supplied to Base-N encode is not a byte[]");
		}
		return encode((byte[]) obj);
	}

	/**
	 * Encodes a byte[] containing binary data, into a String containing characters in the Base-N alphabet.
	 * Uses UTF8 encoding.
	 *
	 * @param pArray a byte array containing binary data
	 * @return A String containing only Base-N character data
	 */
	public String encodeToString(final byte[] pArray) {
		return StringUtils.newStringUtf8(encode(pArray));
	}

	/**
	 * Encodes a byte[] containing binary data, into a String containing characters in the appropriate alphabet.
	 * Uses UTF8 encoding.
	 *
	 * @param pArray a byte array containing binary data
	 * @return String containing only character data in the appropriate alphabet.
	 */
	public String encodeAsString(final byte[] pArray) {
		return StringUtils.newStringUtf8(encode(pArray));
	}

	/**
	 * Decodes an Object using the Base-N algorithm. This method is provided in order to satisfy the requirements of
	 * the Decoder interface, and will throw a DecoderException if the supplied object is not of type byte[] or String.
	 *
	 * @param obj Object to decode
	 * @return An object (of type byte[]) containing the binary data which corresponds to the byte[] or String
	 * supplied.
	 * @throws DecoderException if the parameter supplied is not of type byte[]
	 */
	public Object decode(final Object obj) throws DecoderException {
		if (obj instanceof byte[]) {
			return decode((byte[]) obj);
		} else if (obj instanceof String) {
			return decode((String) obj);
		} else {
			throw new DecoderException("Parameter supplied to Base-N decode is not a byte[] or a String");
		}
	}

	/**
	 * Decodes a String containing characters in the Base-N alphabet.
	 *
	 * @param pArray A String containing Base-N character data
	 * @return a byte array containing binary data
	 */
	public byte[] decode(final String pArray) {
		return decode(StringUtils.getBytesUtf8(pArray));
	}

	/**
	 * Decodes a byte[] containing characters in the Base-N alphabet.
	 *
	 * @param pArray A byte array containing Base-N character data
	 * @return a byte array containing binary data
	 */
	public byte[] decode(final byte[] pArray) {
		if (pArray == null || pArray.length == 0) {
			return pArray;
		}
		final Context context = new Context();
		decode(pArray, 0, pArray.length, context);
		decode(pArray, 0, EOF, context);
		final byte[] result = new byte[context.pos];
		readResults(result, result.length, context);
		return result;
	}

	/**
	 * Encodes a byte[] containing binary data, into a byte[] containing characters in the alphabet.
	 *
	 * @param pArray a byte array containing binary data
	 * @return A byte array containing only the basen alphabetic character data
	 */
	public byte[] encode(final byte[] pArray) {
		if (pArray == null || pArray.length == 0) {
			return pArray;
		}
		final Context context = new Context();
		encode(pArray, 0, pArray.length, context);
		encode(pArray, 0, EOF, context);
		final byte[] buf = new byte[context.pos - context.readPos];
		readResults(buf, buf.length, context);
		return buf;
	}

	/**
	 * package protected for access from I/O streams
	 *
	 * @param pArray  data
	 * @param pos     pos
	 * @param length  length
	 * @param context context
	 * @author lifeng
	 * @date 2020/3/29 10:37
	 */
	public abstract void encode(byte[] pArray, int pos, int length, Context context);

	/**
	 * package protected for access from I/O streams
	 *
	 * @param pArray  data
	 * @param pos     pos
	 * @param length  length
	 * @param context context
	 * @author lifeng
	 * @date 2020/3/29 10:37
	 */
	public abstract void decode(byte[] pArray, int pos, int length, Context context);

	/**
	 * Returns whether or not the <code>octet</code> is in the current alphabet.
	 * Does not allow whitespace or pad.
	 *
	 * @param value The value to test
	 * @return {@code true} if the value is defined in the current alphabet, {@code false} otherwise.
	 */
	protected abstract boolean isInAlphabet(byte value);

	/**
	 * Tests a given byte array to see if it contains only valid characters within the alphabet.
	 * The method optionally treats whitespace and pad as valid.
	 *
	 * @param arrayOctet byte array to test
	 * @param allowed    if {@code true}, then whitespace and PAD are also allowed
	 * @return {@code true} if all bytes are valid characters in the alphabet or if the byte array is empty;
	 * {@code false}, otherwise
	 */
	public boolean isInAlphabet(final byte[] arrayOctet, final boolean allowed) {
		for (byte b : arrayOctet) {
			boolean flag = !isInAlphabet(b) && (!allowed || (b != PAD) && !isWhiteSpace(b));
			if (flag) {
				return false;
			}
		}
		return true;
	}

	/**
	 * Tests a given String to see if it contains only valid characters within the alphabet.
	 * The method treats whitespace and PAD as valid.
	 *
	 * @param basen String to test
	 * @return {@code true} if all characters in the String are valid characters in the alphabet or if
	 * the String is empty; {@code false}, otherwise
	 * @see #isInAlphabet(byte[], boolean)
	 */
	public boolean isInAlphabet(final String basen) {
		return isInAlphabet(StringUtils.getBytesUtf8(basen), true);
	}

	/**
	 * Tests a given byte array to see if it contains any characters within the alphabet or PAD.
	 * <p>
	 * Intended for use in checking line-ending arrays
	 *
	 * @param arrayOctet byte array to test
	 * @return {@code true} if any byte is a valid character in the alphabet or PAD; {@code false} otherwise
	 */
	protected boolean containsAlphabetOrPad(final byte[] arrayOctet) {
		if (arrayOctet == null) {
			return false;
		}
		for (final byte element : arrayOctet) {
			if (PAD == element || isInAlphabet(element)) {
				return true;
			}
		}
		return false;
	}

	/**
	 * Calculates the amount of space needed to encode the supplied array.
	 *
	 * @param pArray byte[] array which will later be encoded
	 * @return amount of space needed to encoded the supplied array.
	 * Returns a long since a max-len array will require > Integer.MAX_VALUE
	 */
	public long getEncodedLength(final byte[] pArray) {
		// Calculate non-chunked size - rounded up to allow for padding
		// cast to long is needed to avoid possibility of overflow
		long len = ((pArray.length + unencodedBlockSize - 1) / unencodedBlockSize) * (long) encodedBlockSize;
		// We're using chunking
		if (lineLength > 0) {
			// Round up to nearest multiple
			len += ((len + lineLength - 1) / lineLength) * chunkSeparatorLength;
		}
		return len;
	}
}
